Pivoting pin joints for loader linkages and the like are normally lubricated with either grease or oil. Oil lubricated joints are typically preferred because they afford greater load carrying capacity than grease lubricated joints, and they eliminate the routine maintenance needed to grease the joints on a daily or per shift basis. For this reason, oil lubricated joints are commonly referred to as low maintenance or maintenance free joints. However, such maintenance free joints must have an effective sealing system to prevent the loss of lubricating oil from the joint that would otherwise result in joint failure. Reference for instance, Reinsma et al. U.S. Pat. No. 4,961,667 issued Oct. 9, 1990 to Caterpillar Inc., which discloses a typical known pivot joint for loader linkages and the like. This known pivot joint includes a pin extending through a main oil cavity or reservoir and journals defined by bearings at opposite ends of the main oil cavity or reservoir. The main oil cavity and journals contain a predetermined quantity of oil sufficient for at least substantially immersing the pin. The oil is retained in the joint by seals at opposite ends of the bearings, the seals also serving to keep dust, dirt and other foreign matter from entering the joint and contaminating the oil. This latter function is particularly significant when the operating environment for the joint is severe, that is, wherein substantial dust, dirt or other foreign matter is present, such as when the loader is used at a construction site or mine, as a build up of contaminants in the pin joint can contribute to premature failure thereof.
As is also typical of oil filled joints, the oil therein is subject to varying temperatures and will expand when heated and contract when cooled. When the oil expands, if the joint is not sufficiently vented, the fluid in the joint, including the oil and any air or other fluids, can be subjected to compressive loading so as to exert outward pressure on the seals, eventually leading to premature wear thereof and oil leakage. Conversely, when the oil contracts, if the joint is not sufficiently vented, a negative pressure or partial vacuum condition can be created in the joint so as to draw air along with damaging contaminants from the environment through the seals into the joint. Additionally, sometimes when the members joined together by the joint are moved one relative to the other, such as when a heavy load is lifted or dumped, or a hard object is contacted by the implement, a rapid pressure increase or spike can occur in the joint, which should be vented to avoid eventual damage to the seals.
One known proposed solution to the above-described seal related problems is to use seals which exert higher contact pressures against the opposing sealing surfaces. However, these seals are more costly and have operational disadvantages, namely, more friction is created between the seals and the opposing sealing surfaces, which can also result in greater seal wear.
Various relief vent and breather constructions are well know in the art. However, an anticipated problem with using the known relief vent and breather constructions on pin joints is oil loss through the vent or breather when the joint is articulated through angular orientations wherein the vent or breather is at least partially inverted or otherwise brought into contact with the oil in the joint such as by splashing or the like. Additionally, because of the articulation of the joint and the possibility of shock and other severe loading from abrupt contact between the loader bucket with hard objects and the like, a vent or breather used with an oil filled pin joint should be ruggedly constructed, securably mounted, and easily serviceable and/or replaceable as required.
Further, currently, the oil level in oil filled pin joints is determined by measuring a quantity of oil then filling the cavity or reservoir of the pin joint with the measured quantity of oil. However, this is a time consuming process. It is thus desirable to shorten the time required for determining the oil level in a pin joint.
Still further, it would be advantageous to combine the pressure relief or breather and oil measuring aspect of a pin joint in a single device, and to provide interchangeability of different pressure relief or breather devices and dipsticks of different lengths and types.
Reference Haines et al. U.S. Pat. No. 4,067,113 issued Jan. 10, 1978 to Estan Manufacturing Company; and Davison, Jr. et al. U.S. Pat. No. 5,129,422 issued Jul. 14, 1992 to General Motors Corporation, which disclose respectively a dipstick with pressure relief valve and a transmission breather control valve which suffer from many of the above described problems.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.